1. Field of the Invention
This application relates to a rotary fluid flow switch and more specifically to a lightweight rotary sound path selector valve for a musical wind instrument having an acoustic pipe terminating on opposite ends with a mouthpiece and instrument bell, respectively, and having one or more intermediate acoustic pipe segments that can be selectively added into the overall length of the acoustic pipe.
2. General Discussion of the Background
Rotary valves are highly regarded for use in musical wind instruments due to their quick action and relative simplicity of structure as compared to piston type valves.
U.S. Pat. Nos. 4,112,806; 4,213,371; 4,299,156; and 4,469,002 disclose improved rotary sound path selector valves that add few unwanted harmonics to a musical instrument's tone. Valve rotors described therein have at least two acoustic passages extending therethrough which have minimal curvature, no edges in the sound path, and no regions of varying cross-sectional area. The acoustic passages align axially with the instrument's lead pipe, main bore, and slide loop ends so that a minimum of undesired harmonics are added to the tone of the instrument.
Existing instrument valves, however, including those described in the above-cited patents, have a number of potential drawbacks. First, they have rigid rotors and casings that require a certain clearance between the rotor casing and rotor to permit free rotation of the rotor in the casing. Second, to facilitate such rotation and to minimize air leaks at points of connection between passages in the rotor and casing apertures, a lubricant is used, which must be cleaned off the parts and replaced during periodic valve overhauls. Third, rotor clearance must be frequently manually adjusted because it is affected by temperature, moisture, amount of lubricant in the valve, soil content of the lubricant, age of the lubricant in the valve, and other factors. Fourth, existing valves are subject to wear, which reduces the airtightness of connected passages, thereby possibly producing undesirable overtones, and can cause rattling when the valve is operated. Fifth, existing valves are also adversely affected by foreign particles on unyielding rotor and interior casing surfaces which can cause the rotor to seize. Sixth, some existing valves are individually manufactured via complex machining operations which add appreciable cost and limited interchangeability of parts. Finally, existing valves are typically fabricated entirely of metals, which generally require lubrication. All-metal valves are heavy and consequently generally require more effort to operate than one would desire.
Hence, there is a need for a musical instrument acoustic path rotary selector valve that, in addition to having minimally curved acoustic passages, has a low-mass rotor that automatically remains seated on bearing surfaces in the casing, and that dimensionally compensates for wear and environmental changes, thus maintaining seal integrity of rotor apertures to casing apertures without periodic adjustment or maintenance. There is also a need for a musical instrument acoustic path rotary selector valve having a jam-free rotor that is quiet in operation, requires no lubricant, and is manufacturable at low cost.